Dynamic modeling of AC multiple ARCS of EHV post station insulators covered with ice

The present contribution proposes a multi-arc dynamic model to predict the parameters of AC flashover propagating over EHV ice-cover insulators. The model considers the arc as time-dependent impedance consisting of a resistance in series with an inductance. The residual ice layer is specified in terms of an equivalent resistance, where the equivalent surface conductivity is calculated by taking into account the water film flowing over the glass surface. The temporary arc length developing over an ice-covered insulator is calculated through the arc velocity, determined using high-speed image recording techniques. The principal characteristics of flashover, including minimum flashover voltage, leakage current and arc velocity are investigated through the proposed multi-arc dynamic model. The proposed models were successfully validated in the laboratory using station post insulators - typically used in Hydro-Quebec 735 kV substations - under AC voltage based on the standard method presented in IEEE Std 1783. Good agreement was also observed between the flashover voltage calculated from the proposed multi-arc model and those obtained experimentally on ice-covered EHV insulators. The proposed model is helpful for properly designing and selecting the EHV insulators used in cold climate conditions.